Single mode fiber distribution design to maximize capacity and resilience in GPON deployments and use thereof

ABSTRACT

A gigabit passive optical network (GPON) includes: at least one strand of optical fiber optically coupled to a fiber distribution hub and terminating at a termination port, the strand optically coupled to another termination port, the strand thus configured to provide a full duplex optical path for the GPON. A method of communication, a method of testing and a method of configuring a network are disclosed.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of priority to U.S. ProvisionalPatent Application Ser. No. 62/406,156, filed Oct. 10, 2016, the contentof which is incorporated herein by reference in its entirety for anypurpose whatsoever.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The invention disclosed herein relates to designs for fiber opticnetworks, and in particular, to design modifications to a PassiveOptical Network (PON), such as a Gigabit Passive Optical Network (GPON).

2. Description of the Related Art

A variety of technologies enable media communications. Among them arepassive optical networks (PONs). Generally, passive optical networks(PONs) are short-haul networks of fiber-optical cable that provide, forexample, Internet access, voice over Internet protocol (VoIP), anddigital TV delivery in metropolitan areas.

A passive optical network (PON) is a fiber network that uses fiber andpassive components like splitters and combiners rather than activecomponents like amplifiers, repeaters, or shaping circuits. Suchnetworks cost significantly less than those using active components. Themain disadvantage is a shorter range of coverage limited by signalstrength. While an active optical network (AON) can cover a range toabout 100 km (62 miles), a PON is typically limited to fiber cable runsof up to 20 km (12 miles). PONs may also be referred to as “fiber to thehome (FTTH)” networks.

Most current networks implement an architecture referred to as “GigabitPON (GPON).” Gigabit-capable passive optical networks (GPON) aredescribed in an International Telecommunications Union Standard, ITU-TG.984.1 (ITU-T G.984.1 (March 2008)), entitled “Gigabit-capable passiveoptical networks (GPON): General Characteristics,” which is incorporatedby reference herein in its entirety along with related standards as maybe referenced therein or as supplements thereto.

GPON uses optical wavelength division multiplexing (WDM) so a singlefiber can be used for both downstream and upstream data. For example, insome embodiments, a wavelength (λ) of 1490 nm transmits downstream dataand a wavelength of 1310 nm is used for upstream data. A wavelength of1550 nm is reserved for uses such as video transmission.

Generally, fiber to the home (FTTH) networks are point to point low lossfiber optic paths linking a central office with customers. Typically,the central office maintains active (or powered) equipment forcommunication with the customer via a passive optical path. The passiveoptical path may include anywhere from two (2) to sixty four (64)passive optical splitters or more to expand the fiber network.

Most traditional GPON networks currently deployed, do not provide for aservice and protect redundant path that can fail-over to protect in theevent of loss of service on the active path. The expense of providingtwo redundant paths for each customer would more than double the costsof construction, materials, and equipment and maintenance costs.

Additionally, some government entities may regulate the minimum levelsof service that each service provider offers. More often, Service LevelAgreements (SLA's), contracts between the GPON Provider and the enduser/customer dictate the minimum service levels, restoration times, andlevels of redundancy, and penalties for non-performance. Widespreadoutages and long restoration and service recovery times may have seriousconsequences from regulatory agencies, provider reputation, customergoodwill, and costly penalties for the GPON provider. Poor customerservice may be leveraged by other GPON competitors and result in masscustomer exodus.

Traditional fiber networks implementing GPON are inherently vulnerableto service interruptions. This is due their unprotected configurations(not Redundant with Service and Protect fiber paths). A loss of a singlefiber strand failure may affect up to sixty four (64) or more customers,depending on the configuration.

Many GPON construction projects are built with outside contract labor,and poorly supported after commissioning. This leaves the provider andthe GPON network at risk during events such as natural disasters, suchas storms, rodent damage, construction activities, tree and pole damage,power burns and lightning strikes. This risk can be mitigated with acomprehensive emergency maintenance program. Generally, implementationof adequate emergency maintenance programs to address such commonlyoccurring risks require continuous availability of a sizable inventoryof repair fiber reels, equipment and materials, as well as trainedin-house personnel.

What are needed are designs for gigabit passive optical networks (GPON)that streamline restoration efforts. Preferably, the designs provide forpre-staging diverse alternate fiber paths which will become available inthe event of an outage on the original fiber path. Additionally, suchdesigns should provide for enhanced system operation during normaloperational conditions.

SUMMARY OF THE INVENTION

In one embodiment, a gigabit passive optical network (GPON) isdisclosed. The GPON includes: at least one strand of optical fiberoptically coupled to a fiber distribution hub and terminating at atermination port, the strand optically coupled to another terminationport, the strand thus configured to provide a full duplex optical pathfor the GPON.

The termination port may be associated with one of another fiberdistribution hub, an access terminal, an optical network terminationunit and an optical line termination. The strand of optical fiber mayinclude a single-mode optical fiber. Optical coupling of the strand toanother termination port may include a splice to the strand, and thesplice may include one of a fiber loop back plug and an optical fiberjumper, further the splice may include an optical coupling to a pigtailof the strand. The gigabit passive optical network (GPON) may include atleast another fiber distribution hub optically linked to the fiberdistribution hub, and the fiber distribution hub optically linked tofiber distribution hub may be configured in an East West distributiondesign.

In another embodiment, a method for providing communications serviceusing a gigabit passive optical network (GPON), is provided. The methodincludes: configuring the GPON with a plurality of strands of opticalfiber that are optically coupled to at least one fiber distribution huband terminating at respective termination ports, and optically couplingeach one of the strands to another respective termination port, each ofthe strands thus configured to provide a full duplex optical path forthe GPON; communicating optical signals through the GPON; and upon lossof service to a subscriber on a communications pathway, switchingcommunication from a first fiber distribution hub to another fiberdistribution hub to restore service to the subscriber.

Optically coupling the strands of optical fiber may include splicingeach strand to one of a fiber loop back plug and an optical fiberjumper. The method may include switching communication at a splitter ofthe GPON. Optically coupling each one of the strands to anotherrespective termination port may include: selecting, for each one of thestrands, a respective termination port that is associated with one ofanother fiber distribution hub, an access terminal, an optical networktermination unit and an optical line termination.

In yet another embodiment, a method for evaluating performance of agigabit passive optical network (GPON) is provided. The method includes:configuring the GPON with a plurality of strands of optical fiber thatare optically coupled to at least one fiber distribution hub andterminating at respective termination ports, and optically coupling eachone of the strands to another respective termination port, each of thestrands thus configured to provide a full duplex optical path for theGPON; and performing optical time-domain reflectometer (OTDR)measurements at the at least one fiber distribution hub.

In a further embodiment, a method for configuring a gigabit passiveoptical network (GPON) is provided. The method includes opticallycoupling at least one strand of optical fiber to a fiber distributionhub and terminating the strand at a termination port; and opticallycoupling the strand to another termination port, the strand thusconfigured to provide a full duplex optical path for the GPON.

BRIEF DESCRIPTION OF THE DRAWINGS

The features and advantages of the invention are apparent from thefollowing description taken in conjunction with the accompanyingdrawings in which:

FIG. 1 is an schematic diagram depicting aspects of a configuration fora gigabit passive optical network (GPON);

FIG. 2 is a chart depicting typical port assignments for an eight (8)port terminal used in a GPON;

FIG. 3 is a diagram depicting splicing arrangements for distributioncables spanning between fiber distribution hubs (FDH) within a GPON;

FIG. 4 is a diagram depicting fiber assignments for a GPON implementinga design as disclosed herein;

FIG. 5 is a diagram depicting restoration of communications within aGPON implementing a design as disclosed herein and that has suffered asevered feed cable;

FIG. 6 is a diagram depicting restoration of communications within aGPON implementing a design as disclosed herein and that has suffered asevered distribution cable; and

FIGS. 7A, 7B and 7C, collectively referred to herein as FIG. 7, arediagrams depicting aspects of resulting from splicing of a distributioncable according to the teachings herein.

DETAILED DESCRIPTION OF THE INVENTION

Disclosed herein are methods and apparatus for implementations ofsingle-mode optical fiber in a gigabit passive optical network (GPON).Generally, the aspects disclosed herein provide for enhanced capacityand reliability in deployments of GPON. Designs disclosed herein makeuse of GPON system components including, for example, equipment in acentral office (CO), a fiber distribution from the central office (CO)to a fiber distribution hub (FDH), a centralized splitter (that may beimplemented as a single splitter or as distributed (multiple) passiveoptical splitters), fiber distribution cable(s) in one or more fibercable sheaths, fiber terminals, fiber drop cables used to feed eachsubscriber and an optical network terminal (ONT). Designs providedenhance fiber usage between the FDH and the subscribers, and may furtherprovide a diverse path from two (2) or more FDH's for outage preventionand rapid recovery.

More specifically, the designs disclosed herein result in distributionfiber deployments for increasing fiber utilization up to 200% betweenthe FDH and the fiber terminal as well as increases in networkreliability. The increases in network reliability serve to reduce riskof fiber related outages by about 50% and enable expedited fiberrestoration. These advantages may be realized by use of diverse routingand built in patching solutions for the PON circuits from the centraloffice or in the distribution fiber cables.

In order to provide some context for the teachings herein, an exemplaryembodiment of a gigabit passive optical network (GPON) is illustrated inFIG. 1.

In FIG. 1, a gigabit passive optical network (GPON) 100 includes a fiberdistribution hub (FDH) 101. Generally, the fiber distribution hub (FDH)101 is an enclosure that contains connections between fiber optic cablesand passive optical splitters in the GPON 100. The FDH 101 provides aconvenient location for servicing connections, making reconfigurations,and testing of the GPON 100. One example of an FDH 101 is the FDH 4000.Sealed Fiber Distribution Hub, available from CommScope, Inc. ofHickory, N.C. (a description of which is included herewith in anInformation Disclosure Statement (IDS) and incorporated for any purposewhatsoever).

Generally, the FDH 101 is optically coupled to a central office 105 anda plurality of subscribers 150. Optical coupling of the central office105 with the FDH 101 is by a feeder cable 110. Optical coupling of thecentral office 105 with the FDH 101 is by a feeder cable 110. Opticalcoupling of the plurality of subscribers 150 with the FDH 101 is by adistribution cable 104.

In the central office 105, an optical line termination (OLT) 102includes equipment for making external connections to the Internet,content providers and the like. An example of an OLT 102 is the GPONHigh density, High Capacity Optical Line Terminal Platform, model no.760171413, C9264 available from CommScope, Inc. of Hickory, N.C. (adescription of which is included herewith in an Information DisclosureStatement (IDS) and incorporated for any purpose whatsoever).

The distribution cable 104 contains a plurality of individual opticalfibers. In this example, the optical fibers are single-mode opticalfibers. Each of the optical fibers is optically coupled to an accessterminal (AT) 110 by an optical network termination (ONT) 103 (theoptical network termination (ONT) 103 may also be referred to as anoptical network unit (ONU)). Generally, the optical network termination(ONT) 103 provides for conversion of optical signals to electricalsignals suited for processing tasks with conventional processors. Anexample of an optical network unit is GPON Optical Network Unit, modelno. 760172957, CS-9004A, available from CommScope, Inc. of Hickory, N.C.(a description of which is included herewith in an InformationDisclosure Statement (IDS) and incorporated for any purpose whatsoever).Connected to each of the optical network termination (ONT) 103 may beone or more subscribers 150.

In the GPON 100, optical wavelength division multiplexing (WDM) is usedso a single optical fiber can be used for both downstream and upstreamdata. Generally, a wavelength (λ) of 1490 nm transmits downstream dataand a wavelength of 1310 nm is used for upstream data. A wavelength of1550 nm may be used as an overlay for uses such as video transmission.

Although the GPON 100 is disclosed herein with regard to certain uses ofcertain wavelengths, it should be recognized that this is merelyillustrative and is not limiting of the disclosed technology. Forexample, other wavelengths may be used. In addition, communicationsprotocols other than those set forth herein may be employed. Morespecifically, and by way of example, in some embodiments, no overlay isused. Rather, packets may be communicated via time division multipleaccess (TDMA) protocols, and encryption may be employed. A variety ofadjustments from what is set forth herein may be made.

The exemplary embodiment of the GPON 100 that is depicted in FIG. 1 issimplified. It should be recognized that a variety of designs forpassive optical networks (PON) may be implemented. For example, otherdesigns may include, without limitation, additional fiber distributionhub(s) 101, additional distribution cables 104 (which may interconnectFDH), distributed splitting, centralized splitting and other suchcomponents. In some embodiments, such as where multiple FDH 101 areimplemented, communications traffic (and/or related system components)may be designated by directional terminology. In a non-limiting example,where the GPON implements a ring, certain components may be consideredto be “East” or “West,” while fiber and/or signals may be “Eastbound” or“Westbound.” Such designations are merely arbitrary and are conventionsadopted for purposes of explanation only. Use of such terminology is notto imply any physical relationship between components beyond that whichis stated herein.

The GPON 100 may include one or more passive optical splitters betweenthe OLT 102 in the office and the ONT/ONU 103 at the premises of thecustomer 150. In the passive optical splitter 122, no power is requiredto split the optical signal or generate multiple wavelengths of light.Optical splitters 122 may be used to passively split the broadcastdownstream signal (1490, 1550 nm or other wavelength) with derivedsignals (referred to as “splits”) ranging from two (2) to 128 portions.Each output of the splitters 122 are individually connected via a singlefiber to the ONT 103 for a respective customer 150. Data packets arebroadcast on a single fiber (downstream) to the splitter(s) 122 and maybe encrypted so that only the packets intended for each ONT 103 arereceived and processed. In the case of a 32-way split (that is, onefiber split thirty two (32) ways), post-split, each of the thirty two(32) output fibers will have up to thirty two (32) encrypted (AES) datapackets transmitted to all thirty two (32) of the ONT's. However, onlythe designated ONT 103 can decrypt their respective encrypted packet.These splitters 122 in the upstream direction (1310 nm) act as anoptical combiner or aggregator, but instead of broadcasting an upstreamsignal back to the OLT 102, each ONT 103 is assigned their own uniquetimeslot using a format, such as time division multiple access (TDMA),which the OLT 102 can decipher. The use of passive optical splitters 122in the GPON 100 allows for an economical model of optically connectingmultiple customers without dedicating an optical point-to-point circuitbetween the OLT 102 and the ONT 103 for each customer 150.

In some embodiments, a splitter (for example, a 2-way up to a 128-waysplitter) would be located at the FDH 101. The n-way splitter would befed with a fiber from the OLT 102 and be connected to n number of fibersand to n number of ONT/Customers. A 288 FDH can support nine (9) 32-way(1×32) splitters, requiring only nine (9) fiber strands from the OLT102. Thus, an office 105 may be located up to thirty six (36) miles awayand feed up to 288 customers. This design eliminates the need to run a288 count fiber sheath up to thirty six (36) miles, and permitsservicing of each customer only using nine (9) fibers. The FDH 101,nevertheless, feeds 288 customers from the splitters to each ONT 103 ona single fiber via the 288 terminated fiber connection in the FDH 101.

Distributed or cascaded splitters 122 involve the use of one or morepassive optical splitter between the FDH 101 and the ONT 103 for eachrespective customer 150. In some embodiments, design of a given GPON 100limits the maximum number of splits to 32, 64, or 128. The higher thesplit, the lower the data speeds that can be provisioned. For example,with a 32-way split, data speeds of 1 Gbps/1 Gbps would be possibleconcurrently for each of the thirty two (32) customers, whereas with a64-way split the available bandwidth and performance would be about halfthat. By placing on the same circuit an 8-way splitter 122 in onelocation (for example, at the FDH 101) and 4-way splitters 122 in otherlocations (for example, at the pole or side of multi-family house), theoverall split is still thirty two (32). It should be noted, however,that optical splitters create insertion loss or attenuation of theoptical signal, typically about 3.5 dB per 2-way split, a 4-way split isabout 7 dB, an 8-way split is about 10.5, a 16-way split about 14, and32-way split about 17-18 dB. Whether two splitters that total thirty two(32) are cascaded, or one 32-way splitter is used, the total losses arealmost identical. As optical loss budgeting is an important designparameter, most GPON systems have an operating window of between about−5 to −30 dBm.

Using a distributed split design helps to maximize capacity of the FDH101 as well as the distribution fiber 104. To illustrate this, considertwo sixteen (16) unit multiple dwelling unit (MDU) properties. Each MDUis fed by a 288 count FDH 101 with a centralized 32-way splitter. Inorder to service the two MDUs, all thirty two (32) splits would be usedand thirty two (32) strands/ports in the FDH 101 in the distributioncable 104 would be used to provide up to four (4) 8-port terminals witha run of thirty two (32) fiber drops to each unit. Considering the samescenario with a design for distributed splitting, in one embodiment, a2-way splitter would be placed at the FDH 101 and coupled to twodistribution cables 104, one each to the respective MDU's. A 16-waysplitter would be placed at each MDU and each 16-way splitter would befed by a single fiber drop, thus feeding thirty two (32) customers withtwo distribution fibers 104 instead of thirty two (32) strands. In thisdesign, the optical loss is still about 17 dB for each customer 150, butthe FDH 101 still has 286 fibers remaining. In a centralized splitarchitecture, the 288 FDH count correlates to a one-for-one customer(288) count. In a distributed split architecture, the single 288 countFDH 101, can easily feed 1000 customers or more at just a 4× utilizationrate. That is, one distribution fiber 104 and a cascaded splitter 122may serve many customers.

The East-West design is agnostic to either a centralized or distributedarchitecture. In fact, as can be seen by the increase in customer countsat the FDH using the cascading splits, the need for a more resilient andsurvivable fiber design is critical. In addition, the East-West designcan also accommodate non GPON optical circuits such as point-to-pointEthernet circuits which bypass splitters or may include transmit (TX)and receive (RX) paths as well as ring designs.

Generally, cables of optical fiber implemented in the GPON 100 exhibit aphysical appearance of a cable or a ribbon. In some embodiments, thecable of optical fiber may be a grouping of separately sheathedindividual strands of optical fiber. Regardless of form, a fundamentalelement of each cable of optical fiber is a strand of optical fiber.Each strand provides a communications channel, and may be individuallyoptically coupled as well as spliced commensurate with the techniquesdescribed herein as well as others known in the art.

Generally, the GPON 100 makes use of single-mode optical fiber. Asingle-mode optical fiber is an optical fiber designed to carry lightonly directly down the fiber in a transverse mode. All optical signalshave the same mode but may have different frequencies. Multi-modeoptical fiber is less expensive than single-mode optical fiber. Becausemulti-mode optical fiber has a larger core-size than single-mode opticalfiber, the multi-mode optical fiber supports more than one propagationmode. Over longer distances, multi-mode optical fiber is limited bymodal dispersion, while single mode optical fiber is not. Accordingly,while it is possible to implement multi-mode optical fiber in at leastsome portions of the GPON 100, longer distances are usually served bysingle-mode optical fiber.

Traditional distribution fiber designs do not use the A-counts at eachtermination location. In the case of a terminal cut-in with eight (8)ports, the fiber ribbon or strand of optical fiber within a loose buffertube must be physically accessed. The individual fibers are then cut tosplice to a pigtail for each port. In this case, a 144 count opticalfiber would have twelve (12) optical fiber ribbons or twelve (12) buffertubes of twelve (12) loose optical fibers each. The remaining expresseleven (11) ribbons or tubes would be left intact and the four (4)unused optical fibers in the ribbon or tube would be left intact and notcut. The eight (8) strands of optical fiber would be cut and then fusedto the eight (8) pigtails to activate the eight (8) ports. The out endof the eight (8) optical fibers would then be cut dead ahead. At thispoint, the fiber count of the sheath leaving the first terminal would beLG01, 9-144, A, 1-8, to identify the 136 live optical fibers remainingand the eight (8) optical fiber dead count (the “A-count”). At the 18thterminal, the fiber sheath count would be LG01, 137-144, A, 1-136.

Traditional designs for passive optical networks (PON) have attempted toaddress this wasteful A-count in the past. For example, some designshave relied upon customized tapered cables of optical fiber that wouldtaper these fiber counts within the sheath to mirror the deploymentdesign, or accept the incremental A-Counts along the fiber span and usestandard consistent fiber count cables to avoid the lead time penaltiesassociated with customized tapered fiber cables.

Accordingly and among other things, the design incorporates splicing ofan optical fiber connection at a fiber optic terminal port to theEastbound fibers and Westbound fibers, thus eliminating the A-counts andproviding two (2) active ports on the same fiber strand within theterminal. Thus, a single strand of optical fiber may be used to providea full duplex optical path to each subscriber without creating unusedfiber A-Counts within the cable sheath at each terminal splice or cut-inlocation.

The design calls for the termination of at least two (2) ports in eachterminal, so a terminal count is in multiples of two (2, 4, 6 or 8) foran eight (8) port terminal. This enables use of both sides of the strandof optical fiber (East and West). A typical port assignment is depictedin FIG. 2.

In order to accomplish the splicing, the terminal connections of theoptical fiber (commonly referred to as “pigtails”) are spliced to theoptical fiber. Splicing may be by, for example, mechanical techniques orby fusing to each side of the strand of optical fiber. Thus, the portsare looped back on themselves using a port compatible fiber loop backplug or compatible fiber jumper. The loop back plug or jumper can beeliminated by mating each pigtail connector together using a compatibleport bulkhead or alignment sleeve. For example, pigtail connectors LG 01Fiber 1 would be barreled or looped to LG 01 Fiber A1, 2 to A2, 3 to A3,and 4 to A4 in an eight (8) port scenario. See FIG. 3 for a conceptuallevel illustration.

In one embodiment, the pigtails remain looped back until fibercharacterization testing has been completed. At this point, the loopback plugs, jumpers or bulkheads are removed, capped with dust covers,retained and reused for the next East-West build.

Architecture of the GPON can be modified to include multiple FDH thatcan be connected together to provide diverse feeds from the CentralOffice base GPON equipment. In some of these embodiments, each FDH maybe linked with a dedicated restoration fiber connection, such as aribbon with twelve (12) or more optical fibers coupled between each FDH.These linking strands of optical fiber can be used as a pass throughfeed for PON optical fibers if the subtended FDHs cannot be feddiversely. In order to improve system reliability, each linked FDH maybe fed diversely from the Central Office GPON equipment and the linkingoptical fibers may be used for restoration purposes only.

Referring now to FIG. 4, aspects of an exemplary embodiment areillustrated. In this illustration, the GPON 100 includes three FDH 101units. Each FDH 101 includes 288 distribution ports (or “counts”), with144 count distribution cables 104 feeding in two directions (“East” and“West”) from each of the three FDH 101. The optical splitter used is a1×32 way optical splitter. Thus, nine (9) 32 way splitters would beneeded for each FDH 101 in order to meet capacity (to use the 288distribution ports) when using a centralized splitter configuration.

In the example, each FDH 101 is fed with nine (9) PON feed fibers 110and fifteen (15) spares from the Central Office (24 total feed fibers110 and 288 distribution fibers 104 in two separate 144 count sheaths).The 144 count cables will feed East and West of the respective FDH 101to each adjacent FDH 101. In this embodiment, each of the 144 fibercables will include twelve (12) spare fibers reserved for fiberrestoration or pass-throughs to each subtended FDH 101. In thisembodiment, a break in the distribution fiber 104 will only affectservice on half of each terminal. As illustrated, all terminal counts inthis example share fiber equally in East and West distributions.

In this embodiment, the design provides an alternate route to re-feedthe splitter when required without reprogramming GPON services toanother PON. The design streamlines restoration efforts by pre-stagingdiverse alternate fiber paths which are available in the event of anoutage on the original fiber path feeding each FDH. This is advantageousas most traditional GPON networks currently deployed do not provide fora service and protect redundant pathways that can fail-over to “protectmode” in the event of loss of service on the active path. In thesesystems, the expense of providing two redundant paths for each customerwould more than double the costs of construction, materials, andequipment and maintenance costs.

The design helps to build in diverse recovery paths in the event ofsevered optical fiber. This is possible, among other things, due to thenetwork of linked FDH 101. This allows for the “rolling” of PON from theaffected optical fiber to another undamaged optical fiber at the centraloffice and the FDH splitter location. This permits the system operatorto “patch around” a break in the distribution fiber 104, even beforepersonnel are activated to repair the damaged optical fiber in thefield. If all optical fibers of the feeder cable 110 to a given FDH 101have been severed, adjacent linked FDH 101 can re-feed theout-of-service (OOS) FDH 101 by rolling the PON to the adjacent FDH 101and patched over to the OOS FDH 101. Once the PON has been rolled overto the OOS FDH 101, the splitters can be rolled to the newly activatedlinking optical fibers, restoring all downstream subscribers 150 beforerecovery efforts have been completed.

The design adds extra reliability to an unprotected architecture withoutthe expense of a conventional redundant design and provides for rapidservice recovery of the Central Office feeder cable 110 serving theFDH(s) 101. The design also limits the impact of a severed distributionfiber 104 between two adjacent FDH 101 to less than 50% of all customersin that sheath due to the East-West design. By utilizing the samesheath, the East-West terminal counts and dual FDH 101, the designbuilds in a certain level of redundancy, or at the least, resilience andsurvivability and nearly doubles the capacity of each fiber sheath at noadditional cost per homes passed.

Turning to FIG. 5, there is illustrated aspects of a scenario involvingdamage to the feeder cable 110. In this example, LG01, fibers 1-12 aresevered between the central office PON equipment and FDH-1. As a result,132 customer ONT fed from FDH-1 are out-of-service, LG01, fibers 1-5 goout-of-service as well. PON ports 1-5 enter into a loss of signal (LOS)alarm. All services fed from FDH-1 at all terminals (1-36) are affectedand out of service (132 subscribers) while all services fed from FDH-2at all terminals (1-36) are unaffected and in-service (132 subscribers).As a result, personnel are dispatched to the failure location to effectrepairs. The personnel will then patch PONS 1-5 to spare feeder fibersLG02, 6-10 and notify an individual assigned to splicing duties (i.e., a“splicer”). The splicer will check for light on LG02, 6-10 andtemporarily patch to dedicated linking fiber LF01 count 1-5 at FDH-2.The splicer will travel to FDH-1 and check for light on LF01, 1-5 androll the five splitters from LG01 1-5 to LF01, 1-5. All 132 subscriberson FDH-1 will restore once each ONT ranges in (30-90 seconds) with theGPON equipment. Once the LG01 fibers 1-12 have been repaired and tested,the splicers and co techs may “roll” the services back off LF01 1-5.

Recovery of a severed distribution cable 104 may involve the replacementof the damaged section of the fiber (commonly referred to as “pieceout”) or if the fiber damage exceeds more than one section, multiplesections of fiber and any intermediate out-of-service terminals willneed to be replaced. The repair section(s) will require two lap splicesto be “cut in” at each end of the damaged section. If possible thesehigh count (96 or higher) lap splices can be brought down to the groundfor rapid recovery. This will require extra slack fiber to reach theground and each splice closure and coordination between personnel. Anexample of a scenario for repair of a severed distribution cable 104 isdepicted in FIG. 6.

Turning to FIG. 6, there is illustrated aspects of a scenario involvingdamage to the distribution cable 104. In this example, the feeder cables110 serving FDH-1 and FDH-2 are intact. The distribution cable 104 isdamaged between termination 2 (term2) and termination 18 (term 18).Alarm analysis can pinpoint damage to each terminal bracketing the fiberissue. All East bound workers fed from FDH-1 will be unaffected up tothe break in the distribution cable 104, while the Eastbound workersbeyond the severed distribution cable 104 are out-of-service as aresult. All westbound workers from FDH-2 will unaffected up to thesevered distribution cable 104, workers beyond the severed distributioncable 104 are out-of-service as a result. The East-West design minimizesfailures resulting from a break to the distribution cable 104, impactingonly about 50% of the total customers in the span.

FIG. 7 depicts aspects of an implementation of a GPON configuredaccording to the teachings herein. In FIG. 7A, a conventional loopdesign is shown. This is provided to service a series of subscribers,such as those on a cul-de-sac. FIG. 7B depicts a distribution cable 104spanning from the first FDH 101, FDH1 to the second FDH 101, FDH2. InFIG. 7C, two side legs are depicted, and include splices therein.

Having thus introduced embodiments of the design for implementation ofgigabit passive optical networks (GPON), some additional aspects are nowpresented.

The design also allows for two or more FDH's to be fed from diversepaths from the Central Office GPON equipment.

The design provides flexibility to feed each FDH from diverse paths in aservice mode and re-feed each FDH from another path on reserved fibersbetween each FDH when fiber feeds fail or are “open.”

The design also allows for the patch-through of Central Office PON feedfibers to feed other subtended FDH's that cannot be fed directly fromthe central office based fibers. Although this may create a less diversefiber routing, this design may be called for due to field conditions.

Advantageously, the design provides for a doubling of subscriberswithout the use of the reserve fibers between FDH's, or near doubling byreserving the first fiber ribbon in each sheath as a back-up spare forrepair and re-feed purposes.

The design doubling by use of the A-Counts (West) in each sheath, thusallowing personnel to feed each terminal from two or more diverse paths(East & West) and provides for increased reliability of up to 50% ifeither path fails.

The design incorporates the use of “barreling” using a bulkhead port orsmall jumpers to temporarily “loop through” connect each fiber strand ateach terminal, allowing the fiber characterization or end to end testingto be performed at each FDH (East and West).

The design allows for the use of bi-directional optical time-domainreflectometer (OTDR) and loss testing to test and document thecontinuity of the fibers between the FDH's and identify any anomaliesand high loss events in the fiber spans to characterize the fiber beforeservices are turned up. An example of a suitable instrument is the VIAVITberd 2000, and Fiber Connect Options (FB2-FCOMP2-MA) 2 sets requiredfor Bi-Directional Fiber Characterization, available from ViaviSolutions, Inc. of Milpitas, Calif.

This design creates fiber characterization labor savings and costlysetup time between each terminal port and the FDH. The design allows forthe removal of the loop through jumpers at the conclusion of thesuccessful fiber characterization testing. The design also will workwith either a centralized optical split, distributed (cascading) splitsor both, to further maximize customers fed by the available fiberswithin the sheath.

In traditional point to point GPON fiber architecture, each fiber isterminated with a connector at the terminal and the FDH, which requiresthe fiber strand to be cut and spliced through to a pigtail which feedsthe respective ports or fiber connection access points. In a traditionalterminal cut in location, the assigned fiber will be cut in half, andonly one side (West) will be terminated to the port pigtail, and theEast side will be cut dead ahead (A-count) in the sheath and leftun-terminated and underutilized. In contrast, the design disclosedherein eliminates this wasteful practice and terminates the unusedfibers in the A-count to another port pigtail in the same terminal (aneight (8) port terminal in this design would use fibers 1-4 and fibers1A-4A). In order to provide a more diverse terminal count, someembodiments of the design recommend that all odd ports be terminated tofibers 1-4 and even port pigtail be spliced through to the Eastboundfibers (former A-counts) (for example, Port 1-fiber 1, Port 2-fiber 1A,Port 3-fiber 2, Port 4-fiber 2A . . . Port7-fiber 4, Port 8-Fiber 4A).Adjacent ports can be looped back more easily and consecutive portassignments may force alternating the serving FDH, building in diverserouting of each GPON circuit.

In some embodiments, the assignment of each port 1-8 is consecutive tospread the working circuits across both FDHs to provide the most robustdiverse deployment to each terminal.

In some embodiments, the design calls for the termination of both theEast and West fibers to the terminal ports, with half of the ports cutin to the East Side and the other half cut in to the West side. In thisconfiguration, a 144 count fiber cable can feed up to 288 individualcustomers. This design may reserve a twelve (12) fiber ribbon whichwould reduce the total number of customers to be fed from a 144 Countfiber from 288 to 264, to create a more resilient network that can bemore readily restored.

Additionally, the design may be used to maximize usage of any opticalfiber cable. Advantageously, the design lends itself to reduced fibercount cables to provide service to nearly twice the number ofsubscribers in a wider serving area.

The design may be implemented in lieu of the trend of placing larger andlarger fiber cables for GPON deployments, which are often in shortsupply, with some higher count cables requiring lead times of six (6)months or more from the fiber cable manufacturers and suppliers.

The design may be implemented in aerial or buried serviceconfigurations. Aerial environments (pole line) in single runs down asingle street or with side legs or cul-de-sac deployments areadvantageous as lines are easily accessed.

This design effectively reduces the placing cost per homes passed byalmost 50% and fiber cable costs by 50% per homes passed and splicingFiber Characterization End to End testing labor by 75-90% at only two(2) locations (FDH1 and FDH2) instead of the normal thirty six (36)aerial eight (8) port terminal locations.

Fiber characterization can be performed using a pair of off the shelfOptical Time Domain Reflectometers (OTDR) and associated software anddocumentation packages such as the VIAVI T-Berd 2000's and the FiberComplete software package. In-line fiber terminals such as theAFL-1642-XL 8 Port Aerial terminal are examples of non-proprietaryinline terminals that do not require proprietary custom fiber dropcables and can utilize field connectorized fiber drops using low lossSC-APC or SC-UPC mechanical connectors (AFL FastConnects) toeconomically connect the terminal port to the customers premise FiberNID (Network Interface Device).

The design may incorporate the use of new cable sheaths specificallyplaced to distribute fibers in the GPON serving area, and does notpreclude the use of dark fiber for the delivery of any other existing orfuture non-GPON based optical services to each residential or businesslocation passed.

The design may include an end to end fiber span with one low loss fusionpigtail splice at the FDH and another low loss fusion splice (<10 dBm)at the pigtail in the terminal unless there is an intermediate low losslap splice in the span required due to field conditions.

When the East and West spans are coupled with a fiber loopback plug,jumper or barrel and viewed with an OTDR from each terminated FDHlocation, the mechanical connections can be clearly seen, measured to(distance to reflection) and quantified and Pass or Fail determinationscan be made.

With this design, normal end-to-end fiber characterization testing fromeach port in every terminal back to the FDH is no longer required. Dueto the fact that all 144 fibers in the sheath are roughly the samelength and inherent losses at specific test wavelengths, and each havethe same number of low loss fusion splices and the same loopbackreflection at each terminal, the overall end to losses when testedbetween each FDH, any anomalies can be detected, located and corrected.The location of the loopback or terminal on the OTDR traces will varybased on the terminal location on the fiber span, but all acceptancetesting (fiber characterization testing) may now be performed at onlytwo locations (FDH1 and FDH2) instead of a minimum of thirty three (33)to thirty six (36), thus avoiding time consuming end-to-end testsperformed at each eight (8) port terminal location on that 144 countspan.

The design allows for the bi-directional test to be performed at twoground based FDH's in most applications, in all weather conditions asopposed to thirty six (36) or more aerial terminal test location thatmay require traffic control personnel during fair weather testing. Theremoval of the loopback, jumpers or bulkheads following testing willstill be required but will not involve OTDR testing or substantial laborat each terminal.

Although certain example methods, apparatus and articles of manufactureand design have been described herein, the scope of coverage of thisdisclosure is not limited thereto. On the contrary, this disclosurecovers methods, apparatus and articles of manufacture and design fallingwithin the scope of the appended claims either literally or under thedoctrine of equivalents.

Various other components may be included and called upon for providingfor aspects of the teachings herein. For example, additional materials,combinations of materials and/or omission of materials may be used toprovide for added embodiments that are within the scope of the teachingsherein.

A variety of modifications of the teachings herein may be realized. Forexample, it should be recognized that a virtually infinite number ofconfigurations for the GPON may be realized. For example, components maybe varied according to a number used or installed, by style ofconnection, type of connection, wavelengths employed (or not employed),by geometric orientation and/or geographic location, and by other suchvariables. Other components not introduced herein and known to be usedin conjunction with GPON technology, or later devised to work with GPONtechnology may be used as deemed appropriate.

Generally, modifications may be designed according to the needs of auser, designer, manufacturer or other similarly interested party. Themodifications may be intended to meet a particular standard ofperformance considered important by that party.

When introducing elements of the present invention or the embodiment(s)thereof, the articles “a,” “an,” and “the” are intended to mean thatthere are one or more of the elements. Similarly, the adjective“another,” when used to introduce an element, is intended to mean one ormore elements. The terms “including” and “having” are intended to beinclusive such that there may be additional elements other than thelisted elements. As used herein, the term “exemplary” is not intended toimply a superlative example. Rather, “exemplary” refers to an embodimentthat is one of many possible embodiments.

While the invention has been described with reference to exemplaryembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications will be appreciated by those skilled in theart to adapt a particular instrument, situation or material to theteachings of the invention without departing from the essential scopethereof. Therefore, it is intended that the invention not be limited tothe particular embodiment disclosed as the best mode contemplated forcarrying out this invention, but that the invention will include allembodiments falling within the scope of the appended claims.

What is claimed is:
 1. A gigabit passive optical network (GPON)comprising: at least one strand of a plurality of strands of opticalfiber optically connected to a first fiber distribution hub and anaccess terminal, the same at least one strand optically connected to asecond fiber distribution hub and the same access terminal, the at leastone strand thus providing a full duplex optical path in a firstdirection from the first fiber distribution hub to the access terminaland in a second direction from the second fiber distribution hub to thesame access terminal.
 2. The gigabit passive optical network (GPON) asin claim 1, wherein the strand of optical fiber comprises a single-modeoptical fiber.
 3. The gigabit passive optical network (GPON) as in claim1, wherein the optical connecting of the strand comprises a splice tothe strand.
 4. The gigabit passive optical network (GPON) as in claim 3,wherein the splice comprises one of a fiber loop back plug and anoptical fiber jumper.
 5. The gigabit passive optical network (GPON) asin claim 3, wherein the splice comprises an optical connection to apigtail of the strand.
 6. The gigabit passive optical network (GPON) asin claim 1, further comprising at least another fiber distribution huboptically linked to at least one of the fiber distribution hubs.
 7. Thegigabit passive optical network (GPON) as in claim 6, wherein the fiberdistribution hub optically linked to at least one of the fiberdistribution hubs are configured in an East West distribution design. 8.A method for providing communications service using a gigabit passiveoptical network (GPON), the method comprising: configuring the GPON witha plurality of strands of optical fiber that are optically connected toat least a first fiber distribution hub and an access terminal, andoptically connecting each one of the strands to a second fiberdistribution hub and the same access terminal, each of the strands thusproviding a full duplex optical path in a first direction from the firstfiber distribution hubs to the access terminal and in a second directionfrom the second fiber distribution hub to the same access terminal;communicating optical signals through the plurality of strands ofoptical fiber; and upon loss of service to a subscriber on acommunications pathway of a strand of the plurality of strands ofoptical fiber, switching communication from the first fiber distributionhub to the second fiber distribution hub to restore service on the samestrand to the subscriber.
 9. The method for providing communicationsservice using a gigabit passive optical network (GPON) as in claim 8,further comprising switching communication at a splitter of the GPON.10. A method for evaluating performance of a gigabit passive opticalnetwork (GPON), the method comprising: configuring the GPON with aplurality of strands of optical fiber that are optically connected to atleast a first fiber distribution hub and an access terminal, andoptically connecting each one of the strands to a second fiberdistribution hub and the same access terminal, each of the strands thusproviding a full duplex optical path in a first direction from the firstfiber distribution hubs to the access terminal and in a second directionfrom the second fiber distribution hub to the same access terminal;performing optical time-domain reflectometer (OTDR) measurements atleast one fiber distribution hub.
 11. The method for evaluatingperformance of a gigabit passive optical network (GPON) as in claim 10,wherein optically connecting the strands of optical fiber comprisessplicing each strand to one of a fiber loop back plug and an opticalfiber jumper.
 12. A method for configuring a gigabit passive opticalnetwork (GPON), the method comprising: optically connecting at least onestrand of optical fiber to a first fiber distribution hub and opticallyconnecting the at least one strand at an access terminal; and opticallyconnecting the same at least one strand to a second fiber distributionhub and optically connecting the at least one strand at the same accessterminal, the at least one strand thus providing a full duplex opticalpath in a first direction from the first fiber distribution hubs to theaccess terminal and in a second direction from the second fiberdistribution hub to the same access terminal.
 13. A gigabit passiveoptical network (GPON) comprising: a plurality of strands of opticalfiber optically connected to a first fiber distribution hub and anaccess terminal, each of the strands of the plurality of strandsoptically connected to a second fiber distribution hub and the sameaccess terminal, the plurality of strands thus providing a full duplexoptical path in a first direction from the first fiber distribution hubto the access terminal and in a second direction from the second fiberdistribution hub to the same access terminal; wherein one strand of theplurality of strands provides services to a plurality of subscribers onthe GPON.